Please try downloading, extracting, and writing the image to the sd card again. It is possible for the image to get corrupted during these steps. I will try myself in the meantime to verify that the image online is working.
I have confirmed that the image linked above works. If it still doesn’t work for you after going through the imaging process again, I would begin to think that your RPi 3 may have broken. You could perhaps try installing the official Raspbian image to verify what the issue is. I have had an RPi working fine for a long time, then after a simple reboot, it would not work. The ACT light just stayed lit like you describe, even with the sd card image verified to be correct on another working RPi. I ascribed the issues with that unit to ESD damage.
@jorywong - What size SD card are you using? Please note that the current image requires an SD card of 8GB or greater. If you try to flash it to a smaller SD card it will be corrupt.